Methanol-to-Olefin Conversion on Silicoaluminophosphate Catalysts: Effect of Bronsted Acid Sites and Framework Structures
Methanol-to-Olefin Conversion on Silicoaluminophosphate Catalysts: Effect of Bronsted Acid Sites and Framework Structures
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DOI：
10.1021/cs200016u
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发表时间：
2011-04-01
期刊：
影响因子：
12.9
通讯作者：
Li, Landong
中科院分区：
文献类型：
--
作者：
Dai, Weili;Wang, Xin;Li, Landong
合成了具有不同骨架结构和Bronsted酸中心含量的磷酸硅铝（SAPO），即SAPO-34、SAPO-41、SAPO-11和SAPO-46，并研究了它们作为甲醇制烯烃（MTO）催化剂的性能。除了公知的SAPO-34催化剂之外，SAPO-41也表现出良好的MTO性能，在723 K的反应温度下甲醇转化率为100%，轻质烯烃选择性为约70%，其保持高达10 h的运转时间。本文用H-1 MAS NMR谱对磷酸硅铝催化剂的Bronsted酸中心进行了表征。这些研究是用未加载的样品进行的，用于研究OH基团的类型和数量，并且在加载氨后用于确定可接近的布朗斯台德酸位点的量。通过原位紫外维斯光谱、热重-差热分析（TG-DTA）和气相色谱-质谱（GC-MS）对MTO反应过程中在催化剂上形成的吸留有机物种进行了分析。在表征和催化结果的基础上，讨论了硅铝磷酸盐的Bronsted酸中心和骨架结构对催化剂在MTO转化反应中催化性能的影响。酸中心的数量对甲醇的吸附、烃池化合物的形成以及催化剂的失活有重要影响。另一方面，所研究的硅铝磷酸盐的骨架结构影响产物的扩散，从而控制MTO反应的产物选择性。
Silicoaluminophosphates (SAPO) with different framework structures and amounts of Bronsted acid sites, that is, SAPO-34, SAPO-41, SAPO-11, and SAPO-46, were synthesized and studied as catalysts for the methanol-to-olefin (MTO) conversion. Besides the well-known SAPO-34 catalyst, also SAPO-41 exhibits a good MTO performance with a methanol conversion of 100% and a selectivity to light olefins of about 70% at the reaction temperature of 723 K, which maintains up to a time-on-stream of 10 h. The Bronsted acid sites of silicoaluminophosphate catalysts employed in this study were characterized by means of H-1 MAS NMR spectroscopy. These studies were performed with unloaded samples for studying the type and number of OH groups and after loading of ammonia for determining the amount of accessible Bronsted acid sites. The occluded organic species formed on the catalysts during the MTO reaction were analyzed by in situ UV/vis spectroscopy, thermogravimetry-differential thermal analysis (TG-DTA), and gas chromatography-mass spectrometry (GC-MS). On the basis of the characterization and catalytic results, we discuss the effects of Bronsted acid sites and framework structures on the catalytic performance of silicoaluminophosphates in the MTO conversion. The amount of Bronsted acid sites strongly affects the adsorption of methanol and the formation of hydrocarbon pool compounds as well as the catalyst deactivation. On the other hand, the framework structures of the silicoaluminophosphates under study influence the diffusion of products and thus control the product selectivity of the MTO reaction.